The Session Initiated Protocol is a text-based signaling protocol that can be used for controlling networked multimedia communication sessions such as voice and video calls over Internet Protocol (IP). SIP is commonly used for setting up and tearing down voice and video calls between two parties (e.g., unicast sessions) or more than two parties (e.g., multicast sessions) with one or several media streams. SIP is commonly used for large scale multiparty conferencing (e.g., up to hundreds of participants) using multicast techniques. Participants in SIP conferencing may be spread across a varied network topography and may communicate with each other via the SIP conference using numerous protocols including public switched telephone network (PSTN), mobile telephony (e.g., 2 G, 3 G, etc.), wireless broadband, wireline broadband, etc.
Network congestion may occur on shared telecommunications networks when plural users contend for access to the same data-transmission resources. Too much network congestion may lead to what is known as congestive collapse, which curtails the usefulness of the network. Congestion control deals with controlling network traffic entry into a network, so as to avoid congestive collapse by attempting to avoid oversubscription of any of the resources, e.g., processing or link capabilities of the intermediate nodes and networks. Congestion control may also involve taking resource reducing steps, such as reducing the rate of sending packets.